Transformers worksheet with answers

Free printable Transformers worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

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1.Easy

An ideal transformer has 100 turns on its primary winding and 5000 turns on its secondary winding. The primary is connected to a 120 V AC supply. Find the secondary voltage V₂.

N₁ = 100N₂ = 5000V₁ = 120 V

V₂ = V

2.Easy

An ideal transformer has 80 turns on its primary winding and 20 turns on its secondary winding. The primary is connected to a 480 V AC supply. Find the secondary voltage V₂.

N₁ = 80N₂ = 20V₁ = 480 V

V₂ = V

3.Medium

A 10 Ω resistor is connected across the secondary winding of an ideal transformer with a turns ratio N₁:N₂ = 10:1. Find the resistance R_1′ seen looking into the primary winding.

N₁:N₂ = 10:1R_L = 10 Ω

R_1′ = Ω

4.Medium

A single-phase 100 kVA, 4160/480 V transformer operates at its rated load. Treat it as ideal. Find the current I_HV in the high-voltage winding.

S = 100 kVAV₁ = 4160 VV₂ = 480 V

I_HV = A

5.Hard

A single-phase 500 kVA transformer has a core loss of 4000 W and a copper loss of 16000 W at rated load. At what load S_η,max, in kVA, is its efficiency highest?

S = 500 kVAP_core = 4000 WP_cu,fl = 16000 W

S_η,max = kVA

6.Hard

A single-phase 25 kVA transformer has a core loss of 150 W. At rated load and a power factor of 0.8 lagging its efficiency is 97%. Find the full-load copper loss P_cu,fl in watts.

S = 25 kVAP_core = 150 Wpf = 0.8η = 97%

P_cu,fl = W

Answer key

1. V₂ = 6000 V
2. V₂ = 120 V
3. R_1′ = 1000 Ω
4. I_HV = 24.04 A
5. S_η,max = 250 kVA
6. P_cu,fl = 468.6 W

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